This test makes sure:

 * the clock is running at the expected rate
 * (potential) power gating has no effect on the clock

v2:
 - use signed integer for the gpu timestamp diff (Bas)

v3:
 - add test and subtest descriptions (Arek)
 - split the fast and long tests in different subtests (Martin)
 - use igt_stats to compute actual statistics (Chris)

v4:
 - call igt_stats_fini() after finishing with the stats (Petri)

v5:
 - add a human-readable text to asserts (Petri)
 - assert directly on the function call, not its return value (Petri)

Cc: Bas Nieuwenhuizen <redacted>
Signed-off-by: Martin Peres <redacted>
---
 tests/amdgpu/amd_info.c | 86 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/tests/amdgpu/amd_info.c b/tests/amdgpu/amd_info.c
index b8f61e16..d6aea827 100644
--- a/tests/amdgpu/amd_info.c
+++ b/tests/amdgpu/amd_info.c

@@ -43,6 +43,82 @@ static void query_firmware_version_test(void)
                     "Failed to query the firmware version\n");
 }

+static void query_timestamp_test(uint32_t sleep_time, int sample_count)
+{
+       struct amdgpu_gpu_info gpu_info = {};
+       double median, std_err, err_95_conf;
+       igt_stats_t stats;
+       float ns_per_tick;
+       int i;
+
+       igt_stats_init_with_size(&stats, sample_count);
+
+       /* figure out how many nanoseconds each gpu timestamp tick represents */
+       igt_assert_f(amdgpu_query_gpu_info(dev, &gpu_info) == 0,
+                    "Failed to query the gpu information\n");
+       igt_assert_f(gpu_info.gpu_counter_freq > 0,
+                    "The GPU counter frequency cannot be undefined\n");
+       ns_per_tick = 1e9 / (gpu_info.gpu_counter_freq * 1000.0);
+
+       /* acquire the data needed for the analysis */
+       for (i = 0; i < sample_count; i++) {
+               uint64_t ts_start, ts_end, cpu_delta;
+               int64_t gpu_delta;
+               float corrected_gpu_delta;
+               struct timespec ts_cpu;
+
+               igt_assert_f(igt_gettime(&ts_cpu) == 0,
+                            "Failed to read the CPU-provided time");
+
+               igt_assert_f(amdgpu_query_info(dev, AMDGPU_INFO_TIMESTAMP, 8,
+                                              &ts_start) == 0,
+                            "Failed to query the GPU start timestamp\n");
+
+               usleep(sleep_time);
+
+               igt_assert_f(amdgpu_query_info(dev, AMDGPU_INFO_TIMESTAMP, 8,
+                                              &ts_end) == 0,
+                            "Failed to query the GPU end timestamp\n");
+
+               /* get the GPU and CPU deltas */
+               cpu_delta = igt_nsec_elapsed(&ts_cpu);
+               gpu_delta = ts_end - ts_start;
+               corrected_gpu_delta = gpu_delta * ns_per_tick;
+
+               /* make sure the GPU timestamps are ordered */
+               igt_assert_f(gpu_delta > 0,
+                            "The GPU time is not moving or is ticking in the "
+                            "wrong direction (start=%lu, end=%lu, "
+                            "end-start=%lu)\n", ts_start, ts_end, gpu_delta);
+
+               igt_stats_push_float(&stats, corrected_gpu_delta / cpu_delta);
+       }
+
+       /* generate the statistics */
+       median = igt_stats_get_median(&stats);
+       std_err = igt_stats_get_std_error(&stats);
+       err_95_conf = std_err * 1.96;
+
+       /* check that the median ticking rate is ~1.0, meaning that the
+        * the GPU and CPU timestamps grow at the same rate
+        */
+       igt_assert_f(median > 0.99 && median < 1.01,
+                    "The GPU time elapses at %.2f%% (+/- %.2f%% at 95%% "
+                    "confidence) of the CPU's speed\ngpu_counter_freq=%u kHz, "
+                    "should be %.0f kHz (+/- %.1f kHz at 95%% confidence)\n",
+                    median * 100.0, err_95_conf * 100.0,
+                    gpu_info.gpu_counter_freq,
+                    gpu_info.gpu_counter_freq * median,
+                    gpu_info.gpu_counter_freq * err_95_conf);
+
+       /* check the jitter in the ticking rate */
+       igt_assert_f(err_95_conf < 0.01,
+                    "The GPU time ticks with a jitter greater than 1%%, at "
+                    "95%% confidence (+/- %.3f%%)\n", err_95_conf * 100.0);
+
+       igt_stats_fini(&stats);
+}
+
 IGT_TEST_DESCRIPTION("Test the consistency of the data provided through the "
                     "DRM_AMDGPU_INFO IOCTL");
 igt_main

@@ -66,6 +142,16 @@ igt_main
        igt_subtest("query-firmware-version")
                query_firmware_version_test();

+       igt_describe("Check that the GPU time ticks constantly, and at the "
+                    "same rate as the CPU");
+       igt_subtest("query-timestamp")
+               query_timestamp_test(10000, 100);
+
+       igt_describe("Check that the GPU time keeps on ticking, even during "
+                    "long idle times which could lead to clock/power gating");
+       igt_subtest("query-timestamp-while-idle")
+               query_timestamp_test(7000000, 1);
+
        igt_fixture {
                amdgpu_device_deinitialize(dev);
                close(fd);
--

2.30.1